This invention relates to an improvement in the method for growing crystalline materials by seed pulling from a melt.
The art for growing crystalline materials by seed pulling from a melt is well developed. The art is exemplified by the "Czochralski Crystal Growth Method", the "Stepanov Technique", the "Inverted Stepanov Technique"; "Edge-Defined Film-Fed Growth" (EFG process), and modifications of those techniques.
All of these techniques may comprise providing a liquid reservoir supply of the crystalline material by feeding a supply of the material in solid form to the reservoir and heating the contents of the reservoir to melt the material, contacting a seed with the melt in the reservoir or with melt which is fed from the reservoir by capillary action to the surface of a product-shaping member, and causing said melt to solidify on the seed.
These techniques are well documented in the literature such as in: J. V. Stepanov, Soviet Physics--Technical Physics, 29,339 (1959); J. C. Swartz et al, J. Electronic Materials, 4,255 (1975); U.S. Pat. Nos. 3,393,054; 4,090,851; 3,591,348; 3,701,636; 3,471,266; 3,527,574; 3,607,112; 3,650,703; 3,687,633; 3,846,082; 3,826,625; 3,765,843 and 3,853,489.
The crystalline materials manufactured by these techniques, such as of alpha-alumina and silicon, have varying utilities such as optical components, photovoltaic devices and as substrates for epitaxially grown semiconductor materials for integrated circuit devices. The latter application has become particularly significant for crystalline bodies grown by the EFG process.
Other crystalline materials which could be manufactured by these techniques include, but are not limited to, doped varieties of white sapphire such as ruby and blue sapphire, any colored form of crystalline yttrium aluminum garnet, both clear and doped, barium titanate and lithium niobate.
With the sophistication of integrated circuit device technology the internal quality of the crystalline bodies which are used as substrates therefor have become important. A problem with all these techniques is the occurrence of microvoids and/or inclusions within the bulk of the crystalline bodies or materials produced. The density of such defects is commonly on the order of 100-1000 per square centimeter when viewed at 100.times.. When the crystalline product materials are lapped and polished, these defects manifest themselves as pits on the surface of the finished materials, commonly up to 300 per centimeter with the defects ranging in size from 1-25 microns in diameter. Such number and size of defects have become unacceptable for currently produced sophisticated integrated circuit devices.
It is an object of this invention to provide an improvement in the method for growing crystalline material by seed pulling from the melt which substantially eliminates such internal defects from the product produced.
It is another object of this invention to provide an improved method as above described which permits continuous feeding of source material into the crucible or furnace without creating such defects in the product.
Still another object of the invention is to provide an improved process as described above which results in higher yields of higher quality product.
Yet another object of the invention is to provide an improvement in the method for growing crystalline materials by seed pulling from a melt which is capable of substantially eliminating such defects over a wide range of crystal pull rates.
Other objects and advantages of the invention will become apparent from the following description.